Sealants are comprised of pigmented or unpigmented synthetic elastomeric polymers which, in the uncured state, constitute pourable or easily extrudable putty-like mastics. When cured, the sealants are transformed into elastomeric materials which are able to expand or contract with the relative motion of the structural elements which the sealant connects and seals. They also form a tight barrier against moisture, gases and chemicals. Such sealants find a wide variety of applications in the building trades industry and the automotive industry where they are widely used to seal fixed window panels and taillight glass panels to coated auto, truck, and bus bodies.
Such sealants include compositions based on polysiloxane polymers as well as others which include polyurethane or polyacrylate polymers. Additionally, modern sealant compositions include one-part and two-part formulations which cure by a variety of chemical mechanisms. One-part sealant compositions generally contain an end-capped base polymer together with a reactive cross-linking agent and, typically, a curing catalyst which promotes the cross-linking reaction either in the presence of heat or atmospheric moisture. Upon application under normal conditions of temperature and moisture, one-part sealants react to form tough, pliable elastomeric seals.
Two-part sealant compositions, on the other hand, comprise two reactive components which are separately packaged and mixed just prior to or at the time of application and react upon mixing to form the semi-rigid sealant bead.
Two-part sealant compositions are less convenient to use since it is necessary to mix the components prior to use or meter the components during application to insure correct proportions if the two components are applied together to form the sealant bead. For this reason, one-part sealants have found wide acceptance in the market. A number of such one-part moisture-curable sealant compositions are known. Because of their convenience and ease of use, there has been increasing demand for such sealants, especially if they possess both good shelf life and rapid curing rates. To enhance the curing rates of moisture-cured sealants, a variety of curing catalysts have been incorporated into such one-part compositions. The following U.S. patents disclose one-part moisture-curable polyurethane based sealant compositions and curing catalysts: 3,779,794 to De Santis (1,2,4-trimethylpiperazine); 3,979,344 to Bryant (dibutyl tin diacetate); 4,038,239 to Coyner, et al. (metallic salts of tin, lead, mercury, or Group VIII such as iron, organo-tin (IV) and organo-lead compounds, and organic amines such as trialkylamines, N-substituted piperidines, N,N,-substituted piperazines, pyridine); 4,469,831 to Bueltjer, et al. (aliphatic or aromatic carboxylic acids, toluenesulfonic acid); and 4,707,515 to Gilch, et al. (organic and inorganic acids, salts of organic acids such as tin naphthenate, tin octoate, tin butyrate, dibutyltin dioctoate, dibutyltin dilaurate, dibutyltin diacetate, iron stearate, lead octoate, or organic amines).